Bandgap reference circuit and sensor chip using the same

ABSTRACT

A bandgap reference circuit including a clamp circuit is provided. The bandgap reference circuit performs the calibration only for one time in a normal mode to store a control code of a reference generator of the clamp circuit. In a suspend mode, the control code is used for controlling the reference generator to cause the clamp circuit to provide a desired source voltage, and a bandgap reference voltage source is shut down to reduce the power consumption.

RELATED APPLICATIONS

The present application is a continuation-in-part application of U.S.patent application Ser. No. 15/499,497 filed on Apr. 27, 2017, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

BACKGROUND 1. Field of the Disclosure

This disclosure generally relates to a bandgap reference circuit and,more particularly, to a bandgap reference circuit and a sensing chipusing the same that shuts down the bandgap reference voltage sourcethereof and provides a source voltage only by a clamp circuit in asuspend mode.

2. Description of the Related Art

FIG. 1 is a conventional power source circuit for providing a sourcevoltage V_(DD) required by a downstream circuit 15. The power sourcecircuit includes a bandgap reference voltage source 11 and a regulator13. The bandgap reference voltage source 11 provides a stable referencevoltage Vref to the regulator 13. The regulator 13 has low staticcurrent Iddq to reduce the power consumption and is used to hold thesource voltage V_(DD). However, in a lower power mode, the regulator 13still requires the power continuously provided by the bandgap referencevoltage source 11 to generate the source voltage V_(DD), such thatsignificant power is still consumed in the low power mode. When thiskind of power source circuit is applied to portable electronic devices,the standby time of the portable electronic devices is shortened.

FIG. 2 is another conventional power source circuit. Compared with theone shown in FIG. 1, the power source circuit in FIG. 2 further includesan operational amplifier 22 in addition to a bandgap reference voltagesource 21 and a regulator 23. The operational amplifier 22 is used as aclamp circuit and to hold the source voltage V_(DD) in a low power mode.In FIG. 2, although the operational amplifier 22 has low static currentIddq and the regulator 23 can be deactivated in the low power mode, thebandgap reference voltage source 21 still continuously operates in thelow power mode.

In addition, in addition to having low static current Iddq (e.g., nanoampere range), the clamp circuit of a bandgap reference circuit has tofulfill the requirements of holding a stable source voltage, a smallcircuit area and working in an allowable voltage range.

Preferably, the clamp circuit of a bandgap reference circuit does notdraw any power from a bandgap reference voltage source in the low powermode. However, it is not easy to achieve this purpose because when thebandgap reference voltage source for providing an accurate referencevoltage Vref is shut down and if the reference voltage Vref has a 10%voltage variation, the source voltage V_(DD) provided by the clampcircuit may change more than 10% to exceed the allowable working voltagerange.

SUMMARY

One object of the present disclosure is to provide a bandgap referencecircuit and an operation method thereof that perform the calibration inthe normal mode.

To achieve the above object, the present disclosure provides a bandgapreference circuit including a bandgap reference voltage source, a clampcircuit and a digital calibration engine. The bandgap reference voltagesource is configured to provide a bandgap voltage. The clamp circuitincludes a reference generator, an operational amplifier, a comparatorand an output switch. The reference generator is configured to generatea first reference voltage. The operational amplifier has a positiveinput terminal, a negative input terminal and an output terminal,wherein the positive input terminal is configured to receive the firstreference voltage, and the output terminal is feedback to the negativeinput terminal via a feedback resistor and configured to output a clampvoltage. The comparator is configured to compare the clamp voltage witha second reference voltage to generate a comparing output, wherein thesecond reference voltage is associated with the bandgap voltage. Theoutput switch is connected to the output terminal of the operationalamplifier and configured to control the outputting of the clamp voltage.The digital calibration engine is configured to adjust, according to thecomparing output, the first reference voltage generated by the referencegenerator to obtain a smallest difference between the clamp voltage andthe second reference voltage.

The present disclosure further provides a bandgap reference circuitincluding a bandgap reference voltage source, a clamp circuit and adigital calibration engine. The bandgap reference voltage source isconfigured to provide a bandgap voltage. The clamp circuit includes areference generator, an operational amplifier, a comparator and anoutput switch. The reference generator is configured to generate a firstreference voltage. The operational amplifier has a positive inputterminal, a negative input terminal and an output terminal, wherein thepositive input terminal is configured to receive the first referencevoltage, and the output terminal is feedback to the negative inputterminal via a feedback resistor and configured to output a clampvoltage. The comparator is configured to compare the first referencevoltage with a second reference voltage to generate a comparing output,wherein the second reference voltage is associated with the bandgapvoltage. The output switch is connected to the output terminal of theoperational amplifier and configured to control the outputting of theclamp voltage. The digital calibration engine is configured to adjust,according to the comparing output, the first reference voltage generatedby the reference generator to obtain a smallest difference between thefirst reference voltage and the second reference voltage.

The present disclosure further provides an operating method of a bandgapreference circuit. The bandgap reference circuit includes a clampcircuit, a bandgap reference voltage source and a digital calibrationengine. The clamp circuit includes a plurality of clamp switches forcontrolling a clamp voltage outputted thereby. The operating methodincludes the steps of: entering a normal mode, in which the clampcircuit is shut down and the digital calibration engine is idle;entering a calibration mode, in which the clamp circuit and the digitalcalibration engine are activated, and the plurality of clamp switchesare arranged as a predetermined conducting state; in the calibrationmode, adjusting, using the digital calibration engine, a conductingstate of the plurality of clamp switches to obtain a smallest differencebetween the clamp voltage and a predetermined source voltage, andstoring, in the digital calibration engine, a control code of theplurality of clamp switches corresponding to the smallest difference;and deactivating the clamp circuit and idling the digital calibrationengine to return to the normal mode.

The present disclosure further provides a sensor chip including areference generator, a clamp circuit, a regulator, a multiplexer and adigital core. The reference generator is configured to provide areference voltage. The clamp circuit is electrically coupled to thereference generator, and configured to receive the reference voltage andhold a source voltage. The multiplexer is electrically coupled betweenthe reference generator and the regulator. The digital core isconfigured to control the regulator and the multiplexer. In a suspendmode, the digital core is configured to control the multiplexer toconnect the reference voltage to the regulator, and the regulator ispowered off. An LDO mode is entered when the digital core receives arising edge or a falling edge of an external clock signal under thesuspend mode. In the suspend mode, the digital core is configured topower on the regulator to provide the source voltage.

The present disclosure further provides a sensor chip including areference generator, a bandgap reference voltage source, a regulator anda switching element. The reference generator is configured to provide areference voltage. The bandgap reference voltage source is configured toprovide a bandgap voltage. The regulator is configured to provide asource voltage. The switching element is coupled between the referencegenerator, the bandgap reference voltage source and the regulator. In anormal mode, the switching element is configured to connect the bandgapvoltage to the regulator to generate the source voltage. In a suspendmode, the switching element is configured to connect the referencevoltage to the regulator.

In the bandgap reference circuit of the present disclosure, diodesformed by the diode connected transistor are used as resistors to reducean occupied area by the circuit. Although this kind of diodes is stillinfluenced by the manufacturing process, the process variation isdiminished after the calibration.

In the bandgap reference circuit of the present disclosure, as thebandgap reference voltage source and the regulator are shut down in thelow power mode or suspend mode, the power consumption of the circuit issignificantly reduced.

In the bandgap reference circuit of the present disclosure, as thecomparator is used for once in the calibration mode and not used forcomparison during most of the time, the comparator is sharable withother circuit functions to effectively utilize the circuit component.

In the bandgap reference circuit of the present disclosure, a sourcevoltage is more accurately set and has a lower voltage variation in asuspend mode, the source voltage can be arranged at a lower level, e.g.,1 volt rather than 1.5 volts, to reduce the leakage current in thesuspend mode.

In the bandgap reference circuit of the present disclosure, thecalibration on the source voltage provided by the clamp circuit isautomatically accomplished in the normal mode, and thus the wafer orchip level trimming is no longer required to effectively reduce the costof testing and production.

The bandgap reference circuit of the present disclosure is preferablyadapted to portable electronic devices that need to reduce the powerconsumption as much as possible, such as the cellphone, tablet computerand wireless mouse.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and novel features of the present disclosurewill become more apparent from the following detailed description whentaken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram of a conventional power source circuit.

FIG. 2 is a block diagram of another conventional power source circuit.

FIG. 3 is a block diagram of a bandgap reference circuit according toone embodiment of the present disclosure.

FIG. 4 is a partial circuit diagram of a reference generator of a clampcircuit according to one embodiment of the present disclosure.

FIG. 5 is a partial circuit diagram of a reference generator of a clampcircuit according to another embodiment of the present disclosure.

FIG. 6A is a partial circuit diagram of a reference generator of a clampcircuit according to an alternative embodiment of the presentdisclosure.

FIG. 6B is an equivalent circuit of FIG. 6A.

FIG. 7 is a block diagram of a bandgap reference circuit according toanother embodiment of the present disclosure.

FIG. 8 is a flow chart of an operating method of a bandgap referencecircuit according to one embodiment of the present disclosure.

FIG. 9 is the operating state of an operating method of a bandgapreference circuit according to one embodiment of the present disclosure.

FIG. 10 is a block diagram of a bandgap reference circuit according toan alternative embodiment of the present disclosure.

FIG. 11 is a current source bank of a reference generator of a clampcircuit according to one embodiment of the present disclosure.

FIG. 12 shows communication between a host controller and a slave chip.

FIG. 13 is a block diagram of a bandgap reference circuit according toanother embodiment of the present disclosure.

FIG. 14A is a timing diagram of the regulator control using an I2Ccommunication protocol in the embodiment of the present disclosure.

FIG. 14B is a timing diagram of the regulator control using an SPIcommunication protocol in the embodiment of the present disclosure.

FIG. 15 is a schematic diagram of turning ON/OFF a regulator accordingto the I/O activity in the embodiment of the present disclosure.

FIG. 16 is a schematic diagram of turning ON/OFF a regulator accordingto the I/O activity and reference clock signal in the embodiment of thepresent disclosure.

FIG. 17 is another schematic diagram of turning ON/OFF a regulatoraccording to the I/O activity and reference clock signal in theembodiment of the present disclosure.

FIG. 18 is an alternative schematic diagram of turning ON/OFF aregulator according to the I/O activity and reference clock signal inthe embodiment of the present disclosure.

FIG. 19 is a schematic diagram of turning ON/OFF a regulator accordingto the I/O activity, reference clock signal and counting number in theembodiment of the present disclosure.

FIG. 20 is the operating state of a bandgap reference circuit accordingto another embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENT

It should be noted that, wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Referring to FIG. 3, it is a block diagram of a bandgap referencecircuit 300 according to one embodiment of the present disclosure. Thebandgap reference circuit 300 includes a bandgap reference voltagesource 31, a clamp circuit 32, a regulator 33 and a digital calibrationengine 34. The bandgap reference circuit 300 is used to provide a sourcevoltage V_(DD) to a downstream circuit 35, wherein the downstreamcircuit 35 includes, for example, a digital core. The source voltageV_(DD) is, for example, smaller than or equal to 1 volt, but not limitedto. If the calibration is performed properly, the source voltage V_(DD)may be set at a lower voltage level.

In the embodiment of the present disclosure, as the calibrated clampvoltage Vclamp outputted by the clamp circuit 32 is almost equal to thedesired source voltage V_(DD) and has a small voltage variation, thedownstream circuit 35 uses a lower source voltage V_(DD). As the clampcircuit 32 is designed to have low power consumption, the leakagecurrent is reduced by providing the source power V_(DD) only by theclamp circuit 32 in a low power mode (or suspend mode).

The bandgap reference voltage source 31 is used to provide a bandgapvoltage Vbg1 not sensitive to the process, voltage and temperature(PVT). The bandgap reference voltage source 31 also provides a referencevoltage to other circuits, e.g., the regulator 33. The regulator 33 iscoupled between the clamp circuit 32 and the downstream circuit 35, andused to hold the source voltage V_(DD) firmly and not being influencedby loading current within a predetermined range. The regulator 33 mayuse a proper regulator without particular limitations as long as theused regulator operates in a normal mode and can be shut down in a lowpower mode.

The clamp circuit 32 includes a reference generator 321, an operationalamplifier 323, a comparator 325, an output switch SW1, a feedbackresistor R1 and a ground resistor R2, wherein the feedback resistor R1and the ground resistor R2 are formed by transistors to reduce thecircuit area.

The reference generator 321 is used to generate an adjustable firstreference voltage Vref1. In one embodiment, the reference generator 321includes a reference current source and a diode bank D1. The referencecurrent source is used to generate a reference current Iref to the diodebank D1, wherein the reference current Iref is preferably within a nanoampere range (e.g., 200 nA) and provided by a standard constanttransconductance (Gm) circuit. The diode bank D1 is shown in FIGS. 4-5for example, and each of the diodes D0-Dn (e.g., formed by diodeconnected transistor) or each of the serially connected diode groupsD0′-Dn′ has different width/length ratio from another and connects toone clamp switch 321 s. By controlling different connection states of aplurality of clamp switches 321 s, the first reference voltage Vref1generated by the reference generator 321 is changeable. As each diodepath is connected to ground, the diodes are not influenced by thevoltage variation. In another embodiment, the reference generator 321includes a reference current source and a transistor bank. Thetransistor bank is connected as shown in FIG. 6A, and FIG. 6B is anequivalent circuit of the transistor bank in FIG. 6A. Similarly, bycontrolling different connection states of a plurality of clamp switches321 s, the first reference voltage Vref1 generated by the referencegenerator 321 is changeable.

In the above embodiments, the diodes or transistors are used to replacethe accurate resistors (e.g., poly resistors) such that the areaoccupied by the resistive circuit is reduced in the nano ampere range.It should be mentioned that the connections of the diodes, transistorsand clamp switches 321 s are not limited to those shown in FIGS. 4-6B.Their connection may be properly arranged without particular limitationsas long as the first reference voltage Vref1 generated by the referencegenerator 321 is step-changed by changing the connection state of theclamp switches 321 s.

The operational amplifier 323 has a positive input terminal (+), anegative input terminal (−) and an output terminal. The positive inputterminal receives the first reference voltage Vref1 generated by thereference generator 321. The output terminal is feedback to the negativeinput terminal via the feedback resistor R1, and used to output a clampvoltage Vclamp. The ground resistor R2 is connected between the negativeinput terminal of the operational amplifier 323 and ground (e.g., FIG. 3showing one end of the ground resistor R2 being connected to the groundand the other end being connected to the feedback resistor R1). Therelationship between the clamp voltage Vclamp and the first referencevoltage Vref1 is written as equation 1:Vclamp=Vref1×(1+R1/R2)  equation 1

The comparator 325 is used to compare the clamp voltage Vclamp with asecond reference voltage Vref2 to generate a comparing output Cout,wherein the second reference voltage Vref2 is associated with thebandgap voltage Vbg1. In this embodiment, said second reference voltageVref2 associated with the bandgap voltage Vbg1 is referred to that thesecond reference voltage Vref2 is equal to the bandgap voltage Vbg1 orthe second reference voltage Vref2 is generated by an analog buffer 36,which is included in the bandgap reference circuit 300, from the bandgapvoltage Vbg1. In other words, the bandgap reference circuit 300 of thisembodiment may or may not include the analog buffer 36 according to thebandgap voltage Vbg1 provided by the bandgap reference voltage source 31and the source voltage V_(DD) to be provided.

In this embodiment, as the clamp voltage Vclamp is calibrated to beclose to or equal to the second reference voltage Vref2 associated withthe bandgap voltage Vbg1, which is not sensitive to PVT, the offsetcaused by the process and voltage variation is diminished. For example,although the reference current Iref and the diode bank D1 are stillsensitive to the process and voltage variation, by adopting thecalibration in the present disclosure, the variation thereof is removed.As for the variation caused by the temperature, it is very tiny comparedwith the offset due to the process.

The output switch SW1 is connected to the output terminal of theoperational amplifier 323 and used to control the outputting of theclamp voltage Vclamp. That is, when the output switch SW1 is conducted,the clamp voltage Vclamp is outputted as the source voltage V_(DD) to beprovided to the downstream circuit 35; when the output switch SW1 is notconducted, the clamp voltage Vclamp is only compared with the secondreference voltage Vref2 without being outputted. The output switch SW1,for example, receives a control signal from the downstream circuit 35 tobe conducted in the low power mode but not conducted in other modes. Theregulator 33 is coupled between the output switch SW1 and the downstreamcircuit 35.

The digital calibration engine 34 is used to adjust the first referencevoltage Vref1 generated by the reference generator 321 according to thecomparing output Cout to cause the clamp voltage Vclamp to have asmallest difference with respect to or be equal to the second referencevoltage Vref2 (or the bandgap voltage Vbg1 when the analog buffer 36 isnot implemented). The digital calibration engine 34 is, for example, adigital signal processor (DSP).

For example, in the embodiments of FIGS. 4-5, the digital calibrationengine 34 changes the connection of the diode bank D1 by controlling theON/OFF of the plurality of clamp switches 321 s to adjust the firstreference voltage Vref1 generated by the reference generator 321. In theembodiment of FIG. 6A, the digital calibration engine 34 changes theconnection of the transistor bank by controlling the ON/OFF of theplurality of clamp switches 321 s to adjust the first reference voltageVref1 generated by the reference generator 321.

Referring to FIG. 7, it is a block diagram of a bandgap referencecircuit 700 according to another embodiment of the present disclosure.The difference between the bandgap reference circuit 700 in FIG. 7 andthe bandgap reference circuit 300 in FIG. 3 is at the voltages comparedby the comparators 325 and 725. Functions of the bandgap referencevoltage source 71, regulator 73, reference generator 721, operationalamplifier 721, output switch SW1, feedback resistor R1 and groundresistor R2 are similar to the bandgap reference voltage source 31,regulator 33, reference generator 321, operational amplifier 321, outputswitch SW1, feedback resistor R1 and ground resistor R2 in FIG. 3, andare appreciated by one of ordinary skill in the art according to thedescriptions of FIG. 3.

More specifically in FIG. 7, the comparator 725 is used to compare thefirst reference voltage Vref1 and a second reference voltage to output acomparing output Cout. In this embodiment, the second reference voltageis shown to be directly equal to the bandgap voltage Vbg2 outputted bythe bandgap reference voltage source 71. As described in the aboveembodiment, FIG. 7 may further include an analog buffer (e.g., theelement 36 in FIG. 3) used to convert the bandgap voltage Vbg2 to adifferent second reference voltage depending on a desired value of thesource voltage V_(DD). The digital calibration engine 74 is used toadjust the first reference voltage Vref1 generated by the referencegenerator 721 according to the comparing output Cout to cause the firstreference voltage Vref1 to have a smallest difference with respect to orbe equal to the second reference voltage (e.g., the bandgap voltageVbg2). The method of adjusting the first reference voltage Vref1 isreferred to FIGS. 3 to 6B.

If it is assumed that the source voltages V_(DD) in FIGS. 3 and 7 areidentical, FIG. 3 does not include the analog buffer 36, and theoperational amplifiers 323 and 723 are ideal, the bandgap voltage Vbg2is selected as Vbg1/(1+R1/R2).

Referring to FIG. 8, it is a flow chart of an operating method of abandgap reference circuit according to one embodiment of the presentdisclosure, and the operating method is adaptable to the bandgapreference circuits 300 and 700 of FIGS. 3 and 7 (e.g., the bandgapreference circuit 300 in FIG. 3 being taken as an example forillustration hereinafter). As mentioned above, the bandgap referencecircuit 300 includes a clamp circuit 32, a bandgap reference voltagesource 31, a regulator 33 and a digital calibration engine 34. The clampcircuit 32 includes a plurality of clamp switches (e.g., clamp switches321 s in FIGS. 4-6B) for controlling a clamp voltage Vclamp outputted bythe clamp circuit 32.

The operating method of this embodiment includes a normal mode, acalibration mode and a low power mode, wherein said normal mode isreferred to that the power required by the downstream circuit 35 isprovided by the bandgap reference voltage source 31 and the regulator 33instead of by the clamp circuit 32; in said calibration mode, the powerrequired by the downstream circuit 35 is still provided by the bandgapreference voltage source 31 and the regulator 33 only the digitalcalibration engine 34 stores the control code for controlling thereference generator 321; and said low power mode is referred to that thepower required by the downstream circuit 35 is provided by the clampcircuit 32 instead of by the bandgap reference voltage source 31 and theregulator 33. Accordingly, in the low power mode, the bandgap referencecircuit 300 consumes lower power than the conventional power sourcecircuits.

The operating method of this embodiment includes the steps of: enteringa normal mode, in which a clamp circuit is shut down and a digitalcalibration engine is idle (Step S81); entering a calibration mode, inwhich the clamp circuit and the digital calibration engine areactivated, and a plurality of clamp switches are arranged as apredetermined conducting state (Step S82); in the calibration mode,adjusting, using the digital calibration engine, a conducting state ofthe plurality of clamp switches to obtain a smallest difference betweenthe clamp voltage and a predetermined source voltage, (Step S83-84);storing, in the digital calibration engine, a control code of theplurality of clamp switches corresponding to the smallest difference,and deactivating the clamp circuit and idling the digital calibrationengine to return to the normal mode (Step S85). In other words, theoperating method of this embodiment enters the calibration mode oncefrom the normal mode, and returns to the normal mode after thecalibration mode is ended. Said one-time calibration is referred to thatthe digital calibration engine controls the plurality of clamp switchesfor one time to obtain the smallest difference or controls the pluralityof clamp switches in a step-by-step manner for several times to obtainthe smallest difference depending on actual operations. The digitalcalibration engine 34 controls the clamp switches in any suitable way aslong as the smallest difference is obtainable.

In other embodiments, in facing the quick environmental change orlong-term operation, said calibration mode is entered automaticallyevery predetermined period of time. For example, the calibration mode isentered after the startup procedure accomplishes and the normal mode isentered after the calibration. Then the calibration mode is enteredagain every 30 or 60 minutes, but not limited thereto. Every timeentering the calibration mode, the clamp switches are controlled toobtain a smallest difference between the clamp voltage and apredetermined source voltage. It is possible that values of the smallestdifference obtained in the calibration modes entered at different timesare different from each other due to different switching states of theclamp switches.

Referring to FIGS. 3 and 8-9 together, details of the operating methodof this embodiment are described hereinafter.

Step S81: After the system is turned on, the bandgap reference circuit300, for example, directly enters a normal mode to provide a sourcevoltage V_(DD) required by the downstream circuit 35. As shown in FIG.9, in the normal mode, as the power required in the operation of thedownstream circuit 35 is provided by the bandgap reference voltagesource 31 and the regulator 33, the bandgap reference voltage source 31and the regulator 33 are turned on; whereas, the clamp circuit 32 isshut down and the output switch SW1 is not conducted. The digitalcalibration engine 34 is in an idle state (i.e., only consuming leakagecurrent) to hold the stored control code.

Step S82: In the normal mode, a calibration mode may be entered, e.g.,receiving a control signal from the downstream circuit 35, automaticallyentered after the start-up, automatically entered every predeterminedtime interval (e.g., counted by a counter) or automatically enteredevery time a low power mode being ended. After entering the calibrationmode, the reference generator 321, the operational amplifier 323 and thecomparator 325 are powered up in order to operate. Then, the referencegenerator 321 starts to generate the reference current Iref and aplurality of clamp switches 321 s therein is set at a predeterminedconducting state. For example, the predetermined conducting state is setto cause the first reference voltage Vref1 outputted by the referencegenerator 321 to have a smallest value, a largest value, a middle valueor other values among generable voltage values.

Step S83: The operational amplifier 323 amplifies the first referencevoltage Vref1 to the clamp voltage Vclamp. The comparator 325 comparesthe clamp voltage Vclamp with the second reference voltage Vref2 (i.e.the voltage to be provided to the downstream circuit 35) to generate acomparing output Cout. The digital calibration engine 34 identifieswhether the difference between the clamp voltage Vclamp and the secondreference voltage Vref2 is smallest or not according to the comparingoutput Cout. If yes, the step S85 is entered; if not, the step S84 isentered. In other words, when the clamp voltage Vclamp and the secondreference voltage Vref2 have a smallest difference therebetween, theclamp voltage Vclamp is closest to a predetermined source voltage V_(DD)and has a smallest difference with respect to the predetermined sourcevoltage V_(DD).

Step S84: Then, the digital calibration engine 34 generates digitalsignals (e.g., 4 bits, 8 bits . . . ) to control the ON/OFF of theplurality of clamp switches 321 s of the clamp circuit 321 to outputdifferent first reference voltages Vref1 (e.g., gradually increasing ordecreasing the first reference voltage Vref1). Each connection state ofthe plurality of clamp switches 321 s corresponds to one first referencevoltage Vref1. The operational amplifier 323 amplifies the firstreference voltage Vref1 to the clamp voltage Vclamp. When changing theconnection of the plurality of clamp switches 321 s, the digitalcalibration engine 34 identifies whether the clamp voltage Vclampgradually approaches the second reference voltage Vref2 according to thecomparing output Cout of the comparator 325. If the smallest differenceis not reached, the steps S83 and S84 are repeatedly performed, and thestep S85 is entered till the smallest difference is obtained.

Step S85: When a smallest difference is identified according to thecomparing output Cout, the digital calibration engine 34 records thecontrol code (e.g., digital code) at the same time, and sends a controlsignal to make the bandgap reference circuit 300 return to the normalmode. When the smallest difference is identified, the clamp circuit isdeactivated and the digital calibration engine is idled to return to thenormal mode.

As the clamp circuit 32 is not used to provide the source voltage V_(DD)in both the normal mode and the calibration mode, the output switch SW1is not conducted in both the normal mode and the calibration mode.

In the calibration mode, as the clamp circuit 32 and the digitalcalibration engine 34 are operated to store the control code, the clampcircuit 32 and the digital calibration engine 34 are turned on.Meanwhile, as the bandgap reference voltage source 31 and the regulator33 still provides the source voltage V_(DD), the bandgap referencevoltage source 31 and the regulator 33 are turned on.

The operating method of this embodiment further includes the step of:entering a low power mode (e.g., an electronic device adopting thebandgap reference circuit 300 entering a sleep mode), in which as theclamp circuit 32 is used to provide the source voltage V_(DD), the clampcircuit 32 is turned on and the output switch SW1 is conducted to outputthe clamp voltage Vclamp as the source voltage V_(DD). Meanwhile, thedigital calibration engine 34 controls the reference generator 321 usingthe control code stored in the calibration mode. The bandgap referencevoltage source 31 and the regulator 33 are shut down to reduce thesystem power consumption in the low power mode.

When the above operating method is adapted to the bandgap referencecircuit 700 in FIG. 7, the digital calibration engine 74 identifieswhether a difference between the first reference voltage Vref1 and thesecond reference voltage (e.g., bandgap voltage Vbg2) reaches a smallestvalue, and records the control code of the plurality of clamp switches321 s corresponding to the smallest difference. In other words, when thedifference between the first reference voltage Vref1 and the secondreference voltage is smallest, the clamp voltage Vclamp is closest to apredetermined source voltage V_(DD) and has a smallest difference valuewith respect to the predetermined source voltage V_(DD). Details ofother parts are similar to the above descriptions and thus not repeatedherein.

In addition, it is possible to adjust the first reference voltage Vref1generated by the reference generator 321 in other ways. For examplereferring to FIGS. 10-11, FIG. 10 is a block diagram of a bandgapreference circuit 300′ according to an alternative embodiment of thepresent disclosure. The difference between the bandgap reference circuit300′ in FIG. 10 and the bandgap reference circuit 300 in FIG. 3 is atthe way of changing the first reference voltage Vref1. In FIG. 3, aplurality of clamp switches 321 s is used to change the connection of aplurality of diodes; whereas in FIG. 11, a plurality of clamp switches321 s is used to change the connection of a plurality of referencecurrent sources iref0 to iref(n) so as to change the first referencevoltage Vref1 generated by the reference generator 321′, wherein iref0to iref(n) respectively have different reference current values. In FIG.10, the diode D1 is an unchanged diode. Functions of other elements inFIG. 10 and the operating method of FIG. 10 are similar to those ofFIGS. 3 and 8 only a circuit structure of the reference generator 321′is changed. That is, these embodiments all adjust the generated firstreference voltage Vref1 according to different connection states of aplurality of clamp switches 321 s, and thus identical parts are notrepeated herein.

More specifically, the clamp switches 321 s of the clamp circuit 321 areused to control the connection of a diode bank (as FIGS. 4-5), atransistor bank (as FIGS. 6A-6B) or a current source bank (as FIG. 11).

In the operating method of the present disclosure, when the outputswitch SW1 is conducted, it means that a low power mode is entered, andthus the clamp circuit is turned on but the bandgap reference voltagesource and the regulator are shut down. When the output switch SW1 isnot conducted, it is possible that the normal mode or the calibrationmode is entered; the bandgap reference voltage source and the regulatorare turned on in both modes to provide source voltage V_(DD) to thedownstream circuit, and the clamp circuit is shut down in the normalmode but activated in the calibration mode. That is, the clamp circuitis turned only in the calibration mode but shut down in other timeinterval of the normal mode. The purpose of activating the clamp circuitis to allow the digital calibration engine to be able to store a controlcode for controlling the ON/OFF of the plurality of clamp switches 321 sin the reference generator.

As mentioned above, as a bandgap reference voltage source of theconventional power source circuit still provides a stable source voltagein a low power mode, the power source circuit consumes significant powerin the low power mode. Therefore, the present disclosure furtherprovides a bandgap reference circuit (FIGS. 3, 7 and 10) and anoperating method thereof (FIG. 8) that perform so called one-timecalibration in the normal mode to store a control code of a plurality ofclamp switches, and provides the source voltage only using a clampcircuit and shuts down the bandgap reference voltage source and theregulator in a low power mode to effectively reduce the total powerconsumption of the bandgap reference circuit.

The bandgap reference circuit in the above embodiments is adaptable to asensing device. The sensing device is used as a sensor chip, forexample, for a mouse device, a touchpad or a capacitive touch device.The sensor chip is used as, for example, a slave chip which communicateswith a host controller via a clock signal and data as shown in FIG. 12.The host controller and the sensor chip perform the communication using,for example, an I2C, an SPI, an SMBUS or other serial or parallelcommunication protocols.

When there is no input/output (I/O) activity occurring for apredetermined time interval, the host controller introduces the sensorchip to enter a suspend mode (or referred as a low power mode) to reducethe power consumption. However, when the sensor chip is informed toreturn to a normal mode from the suspend mode, the host controllerusually has to wait for a period of time (e.g., referred as wakeup time)after sending a wakeup command to the sensor chip to wait for thebandgap reference voltage source to wake up. Especially a longer wakeuptime is required when the bandgap reference voltage source has a smallcurrent and large capacitance.

In some embodiments, when the sensor chip is required to support fastread/write events, e.g., reading/writing digital data using burst mode,the sensor chip has to provide an instant response without a wakeuptime. In this scenario, the wakeup time will be an issue.

In some embodiments, the host controller wakes up only a part of thesensor chip (e.g., digital part) to support some events, e.g., updatingthe sensor status, without powering on the whole sensor chip. Thisscenario is referred as light current event.

As mentioned above, in the suspend mode, the source voltage V_(DD) isprovided by the clamp circuit. However, due to its small current andsmall circuit area design, the clamp circuit is not suitable to supportheavy current events, e.g., continuously supporting burst moderead/write. In addition, the sensor chip will not clearly know whetherthe host controller is going to perform the full wakeup, status updateor burst mode read/write without decoding the command or data from thehost controller. If the power is only supported by the clamp circuitwithout waking up the regulator, a clamp voltage clamped by the clampcircuit can slowly decay with the operating time, wherein the decay ratedepends on the capacitance of the clamp circuit (on-chip capacitorgenerally very small). For example, when the reading/writing time of theburst mode extends long (e.g., the memory is large), it is possible thatthe clamp voltage reduces to a level lower than a minimum voltage valuecapable of maintaining the digital and memory state such that problemscan be caused.

Accordingly, the present disclosure further provides a bandgap referencecircuit and a sensor chip using the same that switch quickly from asuspend mode (i.e. a mode powered by the clamp circuit, and the bandgapreference voltage source and the regulator being powered off) to a LDOmode (i.e. powered by the regulator, and the bandgap reference voltagesource not being woken up yet), that quickly support heavy currentevents without a long wakeup time, that respond real-timely withoutdecoding the command or data from the host controller at first, and thatsupport heavy current events for a longer time. In addition, if a fullwakeup is confirmed after the decoding (performed after entering the LDOmode), the bandgap reference voltage source is awoken after the wakeuptime. The present disclosure has a large operating flexibility.

Referring to FIG. 13, it is a block diagram of a bandgap referencecircuit 1300 according to another embodiment of the present disclosure.The bandgap reference circuit 1300 is applicable and included in, forexample, a sensor chip (slave chip) shown in FIG. 12 to communicate withan external host controller. The bandgap reference circuit 1300 savesmore power in a suspend mode (or referred to a low power mode) andswitches to the regulator to enter a LDO (low dropout) mode to provide asource voltage V_(DD) without decoding at first before entering the LDOmode (described by an example below). Meanwhile, after the communicationevent is over, the regulator is turned off to return to the suspendmode. More specifically, the regulator is not necessary to be powered onwhen there is no communication event.

The bandgap reference circuit 1300 includes a reference generator 1321,a bandgap reference voltage source 1301, a clamp circuit 1302, aregulator 1303, a switching element 1307, a digital core 1308, a clockgenerator 1309 and a counter 1310, wherein the counter 1310 may not beimplemented according to different applications.

As mentioned above, the bandgap reference voltage source 1301 is used toprovide a bandgap voltage Vbg in a normal mode. The bandgap referencevoltage source 1301 is implementable by, for example, the bandgapreference voltage source 31 in FIG. 3 or the bandgap reference voltagesource 71 in FIG. 7; and the bandgap voltage Vbg is implementable by,for example, the bandgap voltage Vbg1 or Vbg2 in FIG. 3 or FIG. 7. Inthis embodiment, the bandgap reference voltage source 1301 is poweredoff in both the suspend mode and the LDO mode for reducing the totalpower consumption.

In this embodiment, the LDO mode is considered as an intervening modebetween the suspend mode and the normal mode or considered as a part ofthe suspend mode. It is possible that the bandgap reference circuit 1300returns to the suspend mode from the LDO mode or enters a normal modefrom the LDO mode. For example, the suspend mode is returned when thecommunication events are over, and the normal mode is entered when thefull wakeup (e.g., according to the decoding result) is required.

The reference generator 1321 is used to provide the reference voltageVref1. The reference generator 1321 is implementable, for example, bythe reference generator 321 of FIG. 3, by the reference generator 721 ofFIG. 7 or by the reference generator 321′ of FIG. 10; and the referencevoltage Vref1 is implementable by, for example, the reference voltageVref1 in FIG. 3, 7 or 10. In this embodiment, the reference voltageVref1 is calibrated to be similar to or identical to the bandgap voltageVbg in the normal mode or at background, and one method of thecalibration has been described above (e.g., referring to FIG. 8) andthus details thereof are not repeated herein. In the present disclosure,the reference voltage Vref1 is PVT (process, voltage and temperature)sensitive; while the bandgap voltage Vbg is PVT insensitive.

The clamp circuit 1302 is electrically coupled to the referencegenerator 1321, and used to receive the reference voltage Vref1 in thesuspend mode to hold the source voltage V_(DD). As mentioned above, thesource voltage V_(DD) is used to provide the power required by thedownstream circuit (e.g., the digital core 1308). The “Cap” shown inFIG. 13 indicates an external component or an on-chip capacitor. In oneembodiment, the clamp circuit 1302 includes, for example, the components323, R1 and R2 shown in FIG. 3, but not limited thereto.

If the embodiment in FIG. 13 has the function of calibrating thereference voltage Vref1 as the embodiment does in FIG. 3, the bandgapreference circuit 1300 further includes a comparator 325, an outputswitch SW1 and a digital calibration engine 34, and the details thereofhave been described above and thus details thereof are not repeatedherein.

The regulator 1303 is used to provide the source voltage V_(DD) in thenormal mode and the LDO mode. The regulator 1303 is implementable by,for example, the regulator 33 in FIG. 3 or the regulator 73 in FIG. 7.The regulator 1303 has larger MOS switches than the clamp circuit 1302.

The switching element 1307 is coupled between the reference generator1321, the bandgap reference voltage source 1301 and the regulator 1303,and used to switch, under the control of the digital core 1308, thevoltage to be inputted into the regulator 1303, i.e. the Vref_Ido beingselected as the bandgap voltage Vbg or the reference voltage Vref1. Forexample, FIG. 13 shows that the switching element 1307 is a multiplexer,but not limited thereto, as long as it is a component capable ofselecting one of the bandgap voltage Vbg and the reference voltage Vref1to be provided to the regulator 1303. The regulator 1303 generates thesource voltage V_(DD) based on the input of the reference voltage Vref1or the bandgap voltage Vbg.

The digital core 1308 includes, for example, a digital signal processor(DSP), an application specific integrated circuit (ASIC) or amicrocontroller unit (MCU). In this embodiment, the digital core 1308 isused to control, according to the packet data and clock signal from anexternal host controller, the ON/OFF of the regulator 1303, the ON/OFFof the bandgap reference voltage source 1301, the counting and reset ofthe counter 1310, and the switching function of the switching element1307, and digital core 1308 has a memory for storing digital data. Inone embodiment, the host controller and the sensor chip perform thecommunication using an I2C, an SPI or an SMBUS communication protocol,FIG. 12 shows that the communication includes the transmission of theclock signal and the packet data (e.g., including D0 to Dn).

The clock generator 1309 is used to generate a reference clock signalREF_CLK to be used by the sensor chip in the suspend mode. Preferably,the clock generator 1309 generates a main clock signal in the normalmode and generates the reference clock signal REF_CLK in the suspendmode. The frequency of the main clock signal is preferably much largerthan that of the reference clock signal REF_CLK. Preferably, the periodof the reference clock signal REF_CLK is longer than the length ofpacket data sent from the host controller. The counter 1310 is used tocount one of rising edges or falling edges of the reference clock signalREF_CLK (e.g., the counting number being added by 1 each time a risingedge or a falling edge being detected), and the counting number of thecounter 1310 is reset to 0 by the digital core 1308 (described by anexample below).

Please referring to FIGS. 13 and 20, the operating states in the normalmode and the suspend mode of the present disclosure are describedhereinafter.

In the normal mode, the digital core 1308 controls the bandgap referencevoltage source 1301 and the regulator 1303 to turn on. The switchingelement 1307 connects (e.g., conducting the node 0 of a multiplexer) thebandgap voltage Vbg of the bandgap reference voltage source 1301 to theregulator 1303 to generate the source voltage V_(DD). Meanwhile, thereference generator 1321 is turned off and does not provide thereference voltage Vref1. The clamp circuit 1302 is also turned off. Thereference generator 1321 and the clamp circuit 1302 are turned off by,for example, bypassing with a switching element or not providing powerthereto.

When the sensor chip (or the digital core 1308) does not receive anycommunication event, e.g., not receiving any clock signal or packet datafrom the host controller, over a predetermined time interval, thesuspend mode is entered. As mentioned above, in order to reduce thepower consumption in the suspend mode as much as possible, the bandgapreference voltage source 1301 and the regulator 1303 are both turned offand the reference generator 1321 and the clamp circuit 1302 are bothturned on in the suspend mode. For example, the digital core 1308 turnsoff the bandgap reference voltage source 1301 via a signal PD_BG, andturns off the regulator 1303 via a signal PD_LDO. In addition, thedigital core 1308 switches the connection (e.g., conducting the node 1of a multiplexer) of the switching element 1307 via a signal Vsel, andcontrols the switching element 1307 to connect the reference voltageVref1 to the regulator 1303. In this way, the regulator 1303 is turnedon anytime to provide the source voltage V_(DD) without waiting the longwakeup time of the bandgap reference voltage source 1301.

Referring to FIGS. 14A and 14B, the method of entering the LDO mode isdescribed hereinafter. FIG. 14A is a timing diagram of the regulatorcontrol using an I2C communication protocol in the embodiment of thepresent disclosure, and FIG. 14B is a timing diagram of the regulatorcontrol using an SPI communication protocol in the embodiment of thepresent disclosure. As shown in FIGS. 14A and 14B, in the suspend mode,when the digital core 1308 does not receive any communication event(shown as NO EVENT), the regulator 1303 is turned off (i.e. maintainingthe suspend mode), e.g., a high level of the signal PD_LDO indicatingpower down the regulator 1303, while a low level of the signal PD_LDOindicating power on the regulator 1303; or vice versa. Said notreceiving any communication event herein is referred to that there is nolevel change (rising edge or falling edge) in the external clock signalEXT_CLK (e.g., SCL in FIG. 14A or SCLK in FIG. 14B). When the digitalcore 1308 receives a communication event (e.g., the external clocksignal EXT_CLK in FIGS. 14A and 14B having a falling edge), the LDO modeis entered. In the LDO mode, the digital core 1308 turns on, via thesignal PD_LDO, the regulator 1303 to generate the source voltage V_(DD).As mentioned above, the switching element 1307 has already connected thereference voltage Vref1 to the regulator 1303 when the low power mode isentered. Accordingly, the regulator 1303 can quickly provide the sourcevoltage V_(DD) based on the reference voltage Vref1 when entering theLDO mode.

In the present disclosure, when the digital core 1308 receives therising edge or falling edge of the external clock signal EXT-CLK, theexternal data from the host controller is also received (as shown inFIGS. 14A and 14B). Before entering the LDO mode, the external commandor data has not been decoded by the digital core 1308. In other words,once the digital core 1308 receives the I/O activity from the hostcontroller, the regulator 1303 is immediately powered on to provide thesource voltage VDD such that even heavy current events (e.g., burst moderead/write) are required, the read/write activity is supported withoutwaiting for the long wakeup time and capable of maintaining for a longinterval. In the LDO mode, the regulator 1303 receives the referencevoltage Vref1 to provide the source voltage VDD. The clamp circuit 1302is maintained powered on or powered off in the LDO mode withoutparticular limitations.

When the I/O activity is over, the sensor chip returns to the suspendmode from the LDO mode. Referring to FIG. 15 for example, when eachpacket data (e.g., P0, P1 and P2 in FIG. 15) is over, the signal PD_LDOis returned to the high level (corresponding to the rising edge orfalling edge of the reference clock signal REF_CLK) to turn off theregulator 1303, i.e. return to the suspend mode. However, in someembodiments, said packet data has a very short transmission period(e.g., 500-600 ns, but not limited thereto) to cause the regulator 1303to be turned on and off repeatedly. Preferably, this toggling should beavoided.

Referring to FIG. 16, it is a schematic diagram of turning ON/OFF aregulator according to the I/O activity and reference clock signal inthe embodiment of the present disclosure. In this embodiment, thereference clock signal REF_CLK generated by the clock generator 1309 inthe sensor chip is used as a reference for determining whether theregulator 1303 is turned off in the LDO mode. For example, after theregulator 1303 is turned on (e.g., at the start of the packet data P0)to enter the LDO mode, and when the communication event is over (e.g.,no I/O activity interval during which the external clock signal EXT_CLKdoes not have a rising edge or falling edge) and the reference clocksignal REF_CLK has a level change (e.g., from high level to low level orfrom low level to high level), the digital core 1308 turns off theregulator 1303 and returns to the suspend mode. In this embodiment, theperiod of the reference clock signal REF_CLK is longer than the intervalof the packet data (e.g., the intervals of P0 to PN shown in FIG. 16) soas to effectively use the level change of the reference clock signalREF_CLK to avoid the repeatedly turning on/off of the regulator 1303.

Referring to FIG. 17, it is another schematic diagram of turning ON/OFFa regulator according to the I/O activity and reference clock signal inthe embodiment of the present disclosure. If the communication event isnot over (e.g., during P0 to PN), even though the reference clock signalREF_CLK has the level change, the digital core 1308 does not turn offthe regulator 1303 (FIG. 17 showing PD_LDO maintaining the low level)until the communication event is over (no I/O activity interval) as wellas the reference clock signal REF_CLK has the level change.

Referring to FIG. 18, it is an alternative schematic diagram of turningON/OFF a regulator according to the I/O activity and reference clocksignal in the embodiment of the present disclosure. In some scenarios,if the level change of the reference clock signal REF_CLK happens tooccur between two packet periods (e.g., FIG. 18 showing between P0 andP1, but not limited thereto), the regulator 1303 is turned on againwithin a short time after being turned off. Although this scenario doesnot occur frequently, the present disclosure further provides a methodto avoid this situation by using a counting number of the counter 1310.

Referring to FIG. 19, it is a schematic diagram of turning ON/OFF aregulator according to the I/O activity, reference clock signal andcounting number in the embodiment of the present disclosure. After theregulator 1303 is turned on (e.g., at the start of the packet data P0)in the LDO mode, and when the communication event is over (e.g., no I/Oactivity interval during which the external clock signal EXT_CLK doesnot have a rising edge or falling edge) and the counting number Cn ofthe counter 1310 reaches a predetermined number (e.g., 2 or 3 timeswhich is determined according to the period of the reference clocksignal REF_CLK; the shorter the period, more times being used, thelonger the period, fewer times being used), the digital core 1308 turnsoff the regulator 1303 and returns to the suspend mode. When the counter1310 starts to count (e.g., FIG. 19 showing counting the rising edges ofthe reference clock signal REF_CLK), the digital core 1308 resets thecounting number Cn of the counter 1310 to 0 (e.g., FIG. 19 showing thereset being held when receiving the packet data P1) when receiving a newcommunication event (e.g., new packet data or the corresponding clocksignal). Meanwhile, when the counting number Cn of the counter 1310reaches a predetermined number (e.g., FIG. 19 showing Cn=2), theregulator 1303 is turned off and the counting number Cn of the counter1310 is reset to 0. In the suspend mode, the counter 1310 is kept beingturned off, and the counting is not started until a next LDO mode isentered. Accordingly, it is able to prevent the regulator 1303 frombeing repeatedly turning on/off.

It should be mentioned that the rising edges and falling edges shown inFIGS. 14A to 19 are only intended to illustrate but not to limit thepresent disclosure. In other embodiments, the rising edges in FIGS. 14Ato 19 are replaced by falling edges, and the falling edges are replacedby rising edges according to different applications. In addition,although FIGS. 15 to 19 take the SPI communication protocol as anexample to illustrate, it is not to limit the present disclosure. Inother embodiments, the communication is performed by I2C, SMBUS or otherprotocols. A person skilled in the art would understand how to implementthe present disclosure using other communication protocols according tothe above illustrations based on SPI communication protocol, and thusdetails thereof are not repeated herein.

Although the disclosure has been explained in relation to its preferredembodiment, it is not used to limit the disclosure. It is to beunderstood that many other possible modifications and variations can bemade by those skilled in the art without departing from the spirit andscope of the disclosure as hereinafter claimed.

What is claimed is:
 1. A sensor chip, comprising: a reference generatorconfigured to provide a reference voltage; a clamp circuit, electricallycoupled to the reference generator, and configured to receive thereference voltage and hold a source voltage; a regulator; a bandgapreference voltage source configured to provide a bandgap voltage in anormal mode; a multiplexer electrically coupled between the referencegenerator and the regulator; and a digital core configured to controlthe regulator and the multiplexer, wherein in a suspend mode, thedigital core is configured to control the multiplexer to connect thereference voltage to the regulator, and the regulator is powered off, anLDO mode is entered when the digital core receives a rising edge or afalling edge of an external clock signal in the suspend mode, and thedigital core is configured to power on the regulator to provide thesource voltage in the LDO mode, and the bandgap reference voltage sourceis powered off in the suspend mode and the LDO mode.
 2. The sensor chipas claimed in claim 1, wherein the regulator has larger power MOSswitches than the clamp circuit.
 3. The sensor chip as claimed in claim1, wherein the digital core is further configured to control themultiplexer to connect the bandgap voltage to the regulator to cause theregulator to generate the source voltage in the normal mode.
 4. Thesensor chip as claimed in claim 3, wherein the reference voltage is PVTsensitive, while the bandgap voltage is PVT insensitive.
 5. The sensorchip as claimed in claim 1, wherein the external clock signal is a clocksignal of an I2C, an SPI or an SMBUS communication protocol between thesensor chip and an external host controller.
 6. The sensor chip asclaimed in claim 1, further comprising a clock generator configured togenerate a reference clock signal, wherein in the LDO mode, when theexternal clock signal does not have the rising edge or the falling edgeand the reference clock signal has a level change, the digital core isconfigured to power off the regulator to return to the suspend mode. 7.The sensor chip as claimed in claim 1, further comprising a clockgenerator configured to generate a reference clock signal; and a counterconfigured to count rising edges or falling edges of the reference clocksignal, wherein in the LDO mode, when the external clock signal does nothave the rising edge or the falling edge and the counter counts to apredetermined number, the digital core is configured to power off theregulator to return to the suspend mode.
 8. The sensor chip as claimedin claim 7, wherein the digital core is configured to reset a countingnumber of the counter to 0 when receiving new packet data.
 9. The sensorchip as claimed in claim 1, wherein the digital core is configured toreceive external data when receiving the rising edge or the falling edgeof the external clock signal, but the digital core does not decode theexternal data before entering the LDO mode.
 10. A sensor chip,comprising: a reference generator configured to provide a referencevoltage; a bandgap reference voltage source configured to provide abandgap voltage; a regulator configured to provide a source voltage; aswitching element coupled between the reference generator, the bandgapreference voltage source and the regulator, a clock generator configuredto generate a reference clock signal; a counter configured to countrising edges or falling edges of the reference clock signal; and adigital core configured to control a switching function of the switchingelement and ON/OFF of the regulator, wherein in a normal mode, theswitching element is controlled to connect the bandgap voltage to theregulator to generate the source voltage, and in a suspend mode, theswitching element is controlled to connect the reference voltage to theregulator, and the bandgap reference voltage source is powered off whenthe regulator is powered off in the suspend mode, wherein the regulatoris powered on to generate the source voltage when the digital corereceives a communication event, and when the communication event is overand the counter counts to a predetermined number after the regulator ispowered on, the digital core is configured to power off the regulator.11. The sensor chip as claimed in claim 10, wherein the referencevoltage is PVT sensitive, while the bandgap voltage is PVT insensitive.12. The sensor chip as claimed in claim 10, wherein in the suspend modethe regulator is powered off when the digital core does not receive thecommunication event.
 13. The sensor chip circuit as claimed in claim 10,wherein the digital core is configured to reset a counting number of thecounter to 0 when receiving a new communication event.
 14. The sensorchip as claimed in claim 10, further comprising a clamp circuitelectrically coupled to the reference generator to receive the referencevoltage, and configured to hold the source voltage in the suspend mode.15. The sensor chip as claimed in claim 14, wherein the clamp circuit ispowered on or powered off when the regulator is receiving the referencevoltage to provide the source voltage.
 16. The sensor chip as claimed inclaim 14, wherein the regulator has larger power MOS switches than theclamp circuit.
 17. A sensor chip, comprising: a reference generatorconfigured to provide a reference voltage; a clamp circuit, electricallycoupled to the reference generator, and configured to receive thereference voltage and hold a source voltage; a regulator; a multiplexerelectrically coupled between the reference generator and the regulator;a clock generator configured to generate a reference clock signal; and adigital core configured to control the regulator and the multiplexer,wherein in a suspend mode, the digital core is configured to control themultiplexer to connect the reference voltage to the regulator, and theregulator is powered off, an LDO mode is entered when the digital corereceives a rising edge or a falling edge of an external clock signal inthe suspend mode, and the digital core is configured to power on theregulator to provide the source voltage in the LDO mode, and in the LDOmode, when the external clock signal does not have the rising edge orthe falling edge and the reference clock signal has a level change, thedigital core is configured to power off the regulator to return to thesuspend mode.